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## Light as a Wave: Part 1

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**Light as a Wave: Part 1**SNC2D**What is a wave?**A wave is a disturbance which carries energy from one location to another. The material the disturbance travels through is the medium. The movement of the disturbance is referred to as propagation.**2 Types of Waves**A longitudinal wave is a wave in which the particles of the medium move in a direction parallel to the direction of propagation.**2 Types of Waves**A longitudinal wave is a wave in which the particles of the medium move in a direction parallel to the direction of propagation.**2 Types of Waves**A transverse wave is a wave in which the particles of the medium move in a direction perpendicular to the direction of propagation.**Snapshot of a Wave**The dashed line represents the rest positions of the particles.**Snapshot of a Wave**The positions of maximum displacement are referred to as crests (positive displacement) and troughs (negative). The maximum displacement is the amplitude.**Snapshot of a Wave**The distance between one crest and the next crest (or one trough and the next trough) is the**Snapshot of a Wave**The distance between one crest and the next crest (or one trough and the next trough) is the wavelength, represented by**Snapshot of a Wave**The distance between one crest and the next crest (or one trough and the next trough) is the wavelength, represented by l.**Snapshot of a Wave**The time it takes one complete wavelength to pass a single point is the**Snapshot of a Wave**The time it takes one complete wavelength to pass a single point is the period, represented by**Snapshot of a Wave**The time it takes one complete wavelength to pass a single point is the period, represented by T.**Snapshot of a Wave**The number of complete wavelengths that pass a single point in one second is the frequency, represented by f.**Frequency**Frequency is measured in units of s-1 or Hertz (Hz). “I do not think that the wireless waves I have discovered will have any practical application.”**Wave Speed**The speed of a wave is therefore:**Wave Speed**The speed of a wave is therefore:**Wave Speed**The speed of a wave is therefore:**Wave Speed**The speed of a wave is therefore: Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?**Wave Speed**Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?**Wave Speed**Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?**Wave Speed**Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?**Wave Speed**Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?**Wave Speed**Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?**Wave Speed**Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?**Light is an “EM” wave**Light is actually a transverse wave**Light is an “EM” wave**Light is actually a transverse wave, but the perpendicular-to-propagation disturbance is not of particles of a medium but of the electric and magnetic (EM) fields**The Speed of Light**Because light waves do not need a medium, they can travel through a vacuum (empty space) and do so at the speed of light: c =**The Speed of Light**Because light waves do not need a medium, they can travel through a vacuum (empty space) and do so at the speed of light: c = 3.0 x 108 m/s.**Light-years**A light-year is the distance light would travel in 1 year.**Light-years**A light-year is the distance light would travel in 1 year. Practice Question: How far (in m) is 1.0 light-years?**Light-years**A light-year is the distance light would travel in 1 year. Practice Question: How far (in m) is 1.0 light-years?**The Speed(s) of Light**Light will travel slower in denser media (e.g. glass), but the speed in air is still effectively 3.0 x 108 m/s and**More Practice**p. 391 #1 and 2